1. Field of the Invention
The present invention relates to a radial roller bearing for holding a rotating shaft, a rotating apparatus in use of the radial roller bearing and a method of manufacturing the rotating apparatus.
2. Description of Related Art
Conventionally, as disclosed in JP-A-11-303771, a radial roller bearing has been used in a rotating apparatus for holding a rotating shaft that transmits rotation to a rotary pump such as a trochoid pump.
FIG. 8 shows a partly enlarged schematic view of a rotating apparatus. In the rotating apparatus, a rotating shaft 20 is held by two radial roller bearings 50A and 50B each having no inner race (hereinafter called merely bearing). A trochoid pump (not shown), which is driven by the rotating shaft, is arranged between the bearings 50A and 50B. Each of the bearings 50A and 50B is composed of rollers 51, holder 52 and an outer race 53. The outer race 53 is provided with first and second flanges 55 and 56 formed by bending opposite ends of a cylindrical portion 54 that is in rolling contact with the rollers 51.
It is observed from an endurance test of the rotating apparatus mentioned above that flaking or peeling sometimes occurs in the cylindrical portion 54 of the outer race 53 in a shorter time. As a result of detail investigations of this reason, it is revealed that (1) hardness or strength is different between the cylindrical portion 54 in a vicinity of the first flange 55 and that in a vicinity of the second flange 56 and (2) the radial roller bearing, in which the flaking or peeling occurs in a shorter time, is assembled to orient itself in an axial direction of the rotating shaft 20 so that the rolling surface of the cylindrical portion 54 in the vicinity of the second flange 56, whose hardness or strength is lower, receives radial load F more intensely than that in the vicinity of the first flange 55. That is, the roller bearing is assembled so that the second flange 56 is positioned nearer to the trochoid pump than the first flange 55 in an axial direction of the rotating shaft.
The reason why the hardness or strength is different between the cylindrical portion 54 in a vicinity of the first flange 55 and that in a vicinity of the second flange 56 is described with reference to FIG. 9. FIG. 9 shows a cross sectional view of the outer race 53 before a portion 56xe2x80x2 of the cylindrical portion 54 is bent so as to form the second flange 56 and also shows a hardness change with respect to the rolling surfaces along an axial direction of the outer race 53 after an annealing process. The outer race 53 is made of SPCC (cold rolling steel plate). At first, an end of the cylindrical portion 54 is bent by press forming so as to form the first flange 55. Then, after executing a carbo-nitriding process, the other end of the cylindrical portion 54 (the portion 56xe2x80x2) is annealed. Further, after the rollers 51 and the holder 52 are assembled to the outer race 53, the portion 56xe2x80x2 of the cylindrical portion 54 is finally bent to form the second flange 56.
Since the annealing process is executed as mentioned above, not only the hardness of the second flange 56 is lowered but also the hardness of the cylindrical portion 54 in a vicinity of the second flange 56 is lowered. Accordingly, the hardness of the cylindrical portion 54 in the vicinity of the second flange 56 is lower by 50 to 100 points (Hv) at Vickers hardness than that of the cylindrical portion 54 in the vicinity of the first flange 55.
Next, the reason why the flaking or peeling occurs on the rolling surface of the cylindrical portion 54 in the vicinity of the second flange 56 is described with reference to FIG. 8. The radial load F generated according to an operation of the trochoid pump acts on the rotating shaft 20 so that the rotating shaft 20 is bent at a relative angle xcex8 to a center axis of the bearing 50A or 50B. The radial force F causes high bearing pressure intensively applied to the rolling surface of the cylindrical portion 54 in the vicinity of the second flange 56. Accordingly, the flaking or peeling occurs in a shorter time on the rolling surface of the cylindrical portion 54 in the vicinity of the second flange 56, whose hardness or strength is lower, due to high bearing pressure intensively applied thereto.
As mentioned above, if the bearing is assembled to orient in an axial direction of the rotating shaft 20 so that the radial load F acts on the rolling surface of the cylindrical portion 54 in the vicinity of the first flange 55, whose hardness or strength is higher, the flaking or peeling is unlikely to occur in a shorter time.
An object of the invention is to provide a radial roller bearing, in which hardness or strength of a cylindrical portion of an outer race on an axial end side thereof is different from that on another axial end side thereof, having a structure for distinguishing the axial end of the outer race from the another axial end thereof.
Another object of the invention is to provide a rotating apparatus whose rotating shaft is held by a radial roller bearing having a longer life time endurance.
It is a further object to provide a method of manufacturing the rotating apparatus mentioned above.
To achieve the above object, a radial roller bearing has an outer race and rollers. The outer race has a cylindrical portion and first and second flanges extending radially inward from opposite axial ends of the cylindrical portion, respectively. Hardness or strength of the cylindrical portion in a vicinity of the first flange is different from that in a vicinity of the second flange. The rollers are arranged circumferentially inside the cylindrical portion so as to come in slidable contact therewith.
With the structure of the radial roller bearing mentioned above, a shape of the first flange is different from that of the second flange or a mark is affixed on one of the first and second flanges so as to identify an axial side of the outer race on which either the first flange or the second flange is positioned.
When a pair of the radial roller bearings mentioned above are assembled to a rotating apparatus in which a rotating shaft is rotatably held by the radial roller bearings and a radial load acts on the rotating shaft between the radial roller bearings, first of all, the axial side of the outer race on which the first flange or the second flange of each of the radial roller bearings is positioned can be easily identified based on the shape difference between the first and second flanges or the mark affixed on the one of the first and second flanges. Then, each of the radial roller bearings is easily and confidently assembled so as to orient the outer race in an axial direction of the rotating shaft so that the cylindrical portion in the vicinity of the first flange, whose hardness or strength is higher, receives higher bearing pressure due to the radial load. As a result, flaking or peeling is unlikely to occur in a shorter time so that life time endurance and strength of each of the radial roller bearings is improved.
It is preferable that an inner diameter of the first flange is different from that of the second flange to distinguish the first flange from the second flange.
The inner diameter of the first flange is, preferably, smaller than that of the second flange. If each of the radial roller bearings is assembled so as to orient the outer race axially so that the cylindrical portion in the vicinity of the first flange, whose hardness or strength is higher, receives higher bearing pressure, strength of the radial roller bearing is not jeopardized by the larger inner diameter of the second flange since the cylindrical portion in the vicinity of the second flange receives lower bearing pressure.
Further, to distinguishing the first flange from the second flange, one of the first and second flanges may be provided with a notch or a projection.